1. Field of the Invention
The present invention relates to a vacuum pump used in semiconductor manufacturing apparatus, an electron microscope, a surface analysis apparatus, a mass spectrograph, a particle accelerator, a nuclear fusion experiment apparatus, and so on.
2. Description of the Related Art
When the turbo molecular pump was first developed as a high vacuum pump, there were only full-blade turbo molecular pumps with a blade structure in which the rotor blades are integrated over the entire outer periphery of the rotor. The full-blade turbo molecular pumps, however, have rotor blades with excessive resistance in a low vacuum area, and it was difficult to operate the pump normally. Therefore, improved vacuum pumps using a combination of a turbo molecular pump and a thread groove pump (hereinafter, referred to as a composite vacuum pump) have been developed.
This type of composite vacuum pump includes a rotor 9 which is rotatably disposed in a cylindrical pump case 1, substantially the upper half of which functions as a turbo molecular pump and substantially the lower half of which functions as a thread groove pump, as shown in FIG. 5.
In this type of composite vacuum pump, the part that functions as a turbo molecular pump includes multiple-stage rotor blades 10 arranged on the outer periphery of the rotor 9 and multiple-stage stator blades 11 alternating with the rotor blades 10. With this arrangement, the upper- and lower-stage stator blades 11, which are placed a prescribed distance apart from each other, are positioned and arranged in a radial direction of the pump case 1.
The spacing and arrangement in the radial direction between the stator blades 11 of both the full-blade type and the composite vacuum pumps are performed through multi-stage ring-shaped spacers 60 which are arranged at the inner periphery of the pump case 1. The spacers 60 employ a structure in which the upper and lower spacers 60 and 60 are in engagement with each other in a stack so that lateral misalignment of the spacers 60 can be prevented during the stacking operation in the pump assembly process and the upper and lower spacers 60 and 60 can be arranged in a radial direction of the pump case 1 in the same manner. More specifically, as shown in FIG. 6, the spacers 60 employ a stacked and locked structure in which upper and lower steps 61a and 61b arranged on the inner and outer peripheries thereof, respectively, are in engagement with each other.
The spacer 60, however, is one thin part among the components of the vacuum pump, and it thus becomes deformed easily. Particularly, the related-art spacer 60 having the steps 61a and 61b is thin in most part. Therefore, it becomes deformed more easily and is difficult to process, which leads to an increased cost for the entire pump.
The present invention has been made to solve the above problems. Accordingly, it is an object of the present invention to provide a vacuum pump suitable for reducing the overall pump cost.
In order to achieve the above object, a vacuum pump according to the present invention includes a cylindrical pump case; a rotatable rotor arranged inside the pump case; multistage rotor blades arranged at the upper outer periphery of the rotor; multistage stator blades arranged alternately with the rotor blades at the inner periphery of the pump case; a screw stator shaped to surround the lower outer periphery of the rotor; and ring-shaped spacers placed around the inner periphery of the pump case and interposed between the upper and lower stator blades; wherein the stator blades and the spacers are arranged in the radial direction of the pump case by the contact between the outer periphery portions of the stator blades and the outer periphery portions of the spacers.
According to the invention, with such an arrangement, spacers having a simplified shape that functions only to set the spacing between the stator blades to a prescribed distance.
According to the invention, the walls of the ring-shaped spacers may be rectangular in cross section.
Furthermore, the inner periphery portion of the pump case may form a straight inner cylindrical surface and the outer periphery portion of the stator blades in contact with the inner periphery portion of the pump case and the outer periphery portion of the spacers may form a straight outer cylindrical surface having a diameter equal to each other to be fitted in the inner cylindrical surface of the pump case.
Furthermore, the outer periphery portion of the screw stator may form a straight outer cylindrical surface of a diameter equal to the diameter of the outer cylindrical surfaces of the stator blades and the spacers and may be fitted in the inner periphery portion of the pump case; and the spacer placed most distant from the screw stator may be in contact with the step at the inner cylindrical surface of the pump case to position the spacer and the screw stator along the rotor shaft.
A vacuum pump according to the invention includes a cylindrical pump case; a rotatable rotor arranged inside the pump case; multistage rotor blades arranged at the upper outer periphery of the rotor; multistage stator blades arranged alternately with the rotor blades at the inner periphery of the pump case; a screw stator shaped to surround the lower outer periphery of the rotor; and ring-shaped spacers placed around the inner periphery of the pump case and interposed between the upper and lower stator blades and each having a contact portion for positioning the stator blades in the radial direction of the pump case by the contact with the outer periphery portion of the stator blades; wherein the spacers are arranged in the radial direction of the pump case by the contact between the outer periphery portion of the spacers and the inner periphery portion of the pump case.
In the vacuum pump according to the invention, the spacers may be arranged apart from each other by sandwiching one stator blade between the adjacent spacers, and the outer periphery portion of the spacers may form a straight outer cylindrical surface, at least one end surface thereof forming a plane perpendicular to the outer cylindrical surface.
With such an arrangement, the invention can adopt spacers with a relatively simplified shape having only a function of setting the spacing between the stator blades to a prescribed distance and a function of arranging the stator blades in the radial direction of the pump case.